FIX, coalescestreams incorrect nesting.

IPython/nbconvert/preprocessors/coalescestreams.py

@@ -69,7 +69,7 b' def coalesce_streams(cell, resources, index):'
             last.text += output.text
         else:
             new_outputs.append(output)
-        last = output
+            last = output
 
     cell.outputs = new_outputs
     return cell, resources